Device and method for monitoring the amount of a fluid sprayed across the width of moving material webs for the moistening thereof

ABSTRACT

A method for monitoring the amount of moisture sprayed on a moving material web or a roller across their width, with the width being divided into individual measurement areas includes a measuring step, a storing step and further measuring steps. The measurement is made of local droplet flow of the sprayed liquid in the individual measurement areas, storing the measured values as set values, and again measuring the local droplet flow and comprising it to the set values. The device used includes a counting device and an evaluation unit. The counting device registers droplets of the liquid sprayed on the moving material web in a respective one of the individual measurement areas, and generates a signal per registered droplet which is supplied to the evaluation unit.

This application is based on PCT/EP96/05043 filed Nov. 16, 1996

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates a method for monitoring the amount ofmoisture sprayed across the width of moving material webs for moisteningthem over their width, a device for executing the method and the use ofthis device.

2. Background Art

In the graphic industry it is necessary to moisten rapidly moving paperwebs during defined stages of processing, for example after they havebeen moved through a dryer for the drying of printing ink. The moisturecan either be applied by means of a roller on which a liquid is sprayed,or by directly spraying the liquid on the rapidly moving paper web. Inthe process, the liquid is sprayed by a spraying device over the widthtransversely to the moving direction of the paper web, so that theentire width of the material web is moistened by the liquid. Thistechnique for applying liquids has also proven itself in the textile,foil, non-woven, wood, tissue and other industries. A device for suchmoistening is known from DE 42 27 136 C2, for example. By means of sucha device it is possible to moisten material webs evenly, and liquids ofhigher concentration and reduced water content can be applied to thematerial web. The spraying technique used permits a contactless and evenapplication over the entire width of the material web without theformation of drops, so that gentle and tension-free material processingis provided and therefore the material structure is maintained.

Problems arise if the spraying device does not operate correctly, forexample if one of the several spraying devices arranged next to eachother to cover the full width of the material web does not operatecorrectly or even breaks down. In this case the material web is notcorrectly moistened, or even not moistened at all, in this area, so thatthe material web passed along the spraying device has strips which havebeen differently moistened. Since the moisture content of the materialweb, and therefore the incorrect moistening, can only be detected muchlater in the processing in a step, downstream of the spraying device,and since the material webs are conveyed at very high speeds in therange of 10 m/sec, great lengths of the material web are very rapidlyinsufficiently moistened or even unusable. Known methods for monitoringmoistening therefore require very large amounts of material and arehighly cost-intensive.

SUMMARY OF THE INVENTION

Based on this prior art, it is the object of an present invention toprovide a remedy for the noted difficulty. A method, as well as a devicefor executing the method and the use of the method is intended to bemade available here, by means of which the sprayed-on liquid can besimply and dependably monitored, and possible malfunctions can bedetected early on.

This object is attained in accordance with the present invention by amethod according to which a local droplet flow of the sprayed liquid isrespectively measured for individual measurement areas, storing themeasured local droplet flow values as set values, determining again thelocal droplet flows and comparing them with the previously measured setvalues of the associated measurement area; and a device including acounting device for the registration of droplets of the liquid sprayedin the respective individual measurement areas which can be brought intopositions associated with the measurement areas and can generate onesignal per registered droplet and supplied to an evaluation unitexecuting the method in accordance with claim 7.

By means of the method in accordance with the present invention it ispossible to effectively monitor moistening or the application of liquidson a material web in a simple manner. If a spraying device, by means ofwhich the liquid to be provided for moistening the material web is to besprayed in the direction of the material web width, should not operatecorrectly, so that the material web is not moistened over its width inthe desired manner, this can be immediately detected by means of themethod in accordance with the present invention, by not determining themoisture content of the material web, but the sprayed amount of theliquid to be applied to the material web. By measuring values of localdroplet flow and comparing the measured droplet flow values withpreviously determined set values, additional information is immediatelyprovided regarding which one of the measuring sections operatesinsufficiently. In this case it is possible to preset the toleranceswithin which the local droplet flow values are allowed to diverge fromthe associated set values. A continuous control of the amounts of liquidsprayed on is always provided in this way, so that in case of theappearance of errors in moistening these errors can be evaluated andlocalized and, if necessary, the moistening process can be stopped. Bymeans of this, material waste because of insufficient moistening ofdefined areas of the material web can be prevented.

In an embodiment of the present invention according to which theindividual measurment areas are sequentially covered for determining thelocal droplet flows only one device for determining the local dropletflows is required.

Since as a rule it is intended to moisten the material web over itsentire width, with the initially determined set values are compared witheach other after having been set. If the set values do not agree withindefined tolerances, the spraying devices already operate incorrectlyfrom the start.

According to the embodiment of the present invention, following theinitial determination of the set values, the local droplet flows aremeasured during repeated passages, in which the representative dropletflow of each measurement area is detected once and stored and thatfollowing each passage, the droplet flow values are compared with theset values determined during the first passage.

Each determined droplet flow is compared with its associated set valueimmediately after it has been determined. This indicates a somewhat moreelaborate alternative for permanent monitoring of the sprayed liquid.This alternative has the advantage that incorrect operation can bedetected more rapidly, because it is no longer necessary to wait for acomplete passage as in the embodiment of claim 4.

A signal is provided in case of the deviation of at least one of thedroplet flow values from the associated set value past a preset value.This signal which can be used in different ways, is made available incase of an incorrect operation of the spraying device. It would bepossible, for example, to stop the treatment of the material webimmediately, or it can be used for calling a specialist which firstevaluates the discovered error.

Since the method in accordance with the present invention does notpermit dependable statements regarding the quality of the entire liquidsprayed on the material web, because the sprayed liquid is only locallydetermined in individual measurement areas, the sprayed liquid is onlymonitored for a total outage in the respective measurement areas after adefinite change of the sprayed amounts of liquid, for example afterchanging the web speed during a run. This is practical, since acomparison with initially determined set values is no longer possiblebecause of the lack of the ability to determine absolute amounts ofliquid.

A device for executing the method in accordance with the presentinvention consists of only one counting device, which determines thelocal droplet flow by means of registering individual droplets, and ofan evaluation unit. All droplet flows can be sequentially registered bymeans of the counting device, in that the counting device can be movedinto positions associated with the individual measurement areas. Thisrepresents a structurally simple and cost-efficient solution.

The droplets are advantageously optically registrable for measuring thedroplet flows.

An advantageous embodiment of the counting device has a laser whichilluminates one of the measurement areas associated with the countingdevice, and a photodiode which detects the laser light reflected by thedroplets flying by.

Since the work area in which the material web is moistened becomesgreatly soiled by the sprayed liquid, perforated screens are providedbetween the counting device and the sprayed liquid, so that theoptically operating counting device is soiled as little as possible.

A further protection of the counting device results from the embodimentof the present invention, so that there is a possibility then of openingthe perforated screens only when the measurement area associated withthis perforated screen is intended to be covered by the counting device.

Since often the soiling of the counting device cannot be prevented, acleaning device has been advantageously provided.

So that the function of the counting device can be checked, a checkingdevice is provided, so that a function test can be performed, forexample after a cleaning operation, which provides the assurance thatthe cleaning process has taken place successfully.

The counting device can be quickly and simply brought into positionsassociated with the individual measurement areas for determining theindividual local droplet flows. The preferred monitoring in theimmediate vicinity of the material web, i.e. shortly before the dropletsimpact the material web, is also possible by means of this.

Such an embodiment also permits the simple and space-saving attachmentof the cleaning device and of the testing device.

The device in accordance with the invention can be advantageouslyemployed in the most varied branches of industry.

The present invention will be explained in detail in what follows bymeans of an exemplary embodiment, making reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Represented in the drawings are:

FIG. 1, which is a schematic plan view of a monitoring device inaccordance with the present invention;

FIG. 2, which is a top view of the device of the present invention inaccordance with FIG. 1;

FIG. 3, which is a cross section through a counting device switchedtogether with an evaluation device; and

FIGS. 4 and 5, which show a schematic representation of components of aspraying device.

DESCRIPTION OF A PREFERRED EMBODIMENT

A spraying device 12, by means of which a liquid for moistening a movingmaterial web 14 over a width B can be sprayed in the form of droplets,is represented next to a monitoring device 10 in accordance with thepresent invention is shown in FIGS. 1 and 2. The droplets of liquid arerepresented as short lines or dots 16. Besides the direct moistening ofthe material web 14 with the liquid, as represented in FIGS. 1 and 2,the material web 14 can also be indirectly moistened, in that initiallythe liquid can be sprayed on a roller, and then transferred from thisroller to the material web 14.

The monitoring device 10 has a counting device 18, an evaluation device20 and preferably a cleaning device 22 and a testing device 24.

The counting device 18 is attached to a carriage 26, which is seated,preferably displaceable in the longitudinal direction, on a guidesupport 28. The guide support 28 extends perpendicularly to thedirection of running of the material web 14 preferably at least over thewidth B of the material web, so that the counting device 18 can bepositioned at any location over the entire width of the material web 14.Preferably the guide support 28 is arranged in the immediate vicinity ofthe spraying device 12 and the material web 14, so that the countingdevice 18 can be brought into positions on the guide support 28, inwhich the counting device 18 can count the droplets 16 flying throughthe measurement areas 1, 2 and 3. The measurement areas 1, 2 and 3represented in FIGS. 1 and 2 are only examples. Depending on the width Bof the material web, a larger or smaller number can be provided.

As represented in FIG. 3, the countering device 18 has a light source,preferably a semiconductor later 30, a mirror 32, a lens systemconsisting of lenses 34 and 36, a screen 38 and a photodiode 40. Theseelements of the counting device 18 are housed in a housing 42. In FIG.3, the emitted laser light is represented as beams 44, and the lightreceived by the photodiode as beams 46.

The photodiode 40 is connected via an amplifier 48 and a comparator 50with the evaluation unit 20.

A screen 52 is provided between the counting device 18, which isdisplaceable along the guide support 28, and the sprayed liquid, whichhas openings, preferably round holes, so that perforated screens 54, 55,56 and 57 are formed. The perforated screens 55, 56 and 57 define themeasurement areas 1, 2 and 3, which can be optically covered by thecounting device. Preferably the perforated screens 54 to 57 can beclosed by means of cover plates 60.

The cleaning device 22 is provided in the area of the one end of theguide support 28. The cleaning device 22 can be connected to acompressed air source, not represented, and has a nozzle 62, from whichthe compressed air can flow. Furthermore, testing device 24 is providedat one of the ends of the guide support 28. The testing device 24 has adisk 64, which can be rotated at a defined angular velocity and hasconcentrically arranged openings 66, which preferably are at an evendistance from each other around the circumference. The disk 64 isarranged in such a way that the laser beam 44 of the counting device 18positioned in the area of the end of the guide support 28 can shinethrough the openings 66. When the disk rotates, the laser beam 44 can beinterrupted by means of the disk, which has the openings 66 and rotates.

The method in accordance with the present invention is executed with theaid of the described device in accordance with the invention as follows:

The material web 14 is moved past the spraying device 12, for example inthe direction of the arrow 100. A liquid, for example water or asuitable liquor, is sprayed over the width B by the spraying device 12,so that preferably the entire width B of the material web is covered.

An example of a spraying device 12, which can be preferably employed bymeans of the method of the present invention and the device inaccordance with the present invention, is represented in FIGS. 4 and 5.As indicated in FIG. 4, the spraying device has a plurality of rotatableplates 102, which are arranged next to each other in a row transverselywith respect to the longitudinal direction of the material web 14 andparallel with respect to the guide support 28. As FIG. 5 shows, therotatable plates 102 are preferably attached to the lower end of adriveshaft 104 and have a central cup area 106, which is followed by aradially outward extending flat spray flange 108. For driving therotatable plates 102, their respective driveshafts 104 are connectedwith a motor in a suitable manner, not shown in detail.

In order to fix a defined spraying area for each rotatable plate 102 ofthe spraying device 12, a screen 110 is arranged between the rotatableplates 102 arranged in a row and the material web 14, which has athrough-opening 112 for the liquid to be sprayed on the material web 14in the area of each rotatable plate 102. The spraying areas defined inthis way are fan-shaped and form individual sectors, whichadvantageously adjoin each other flush at the level of the material web,such as shown in FIGS. 1, 2 and 4.

However, a spraying device can also he employed, which has a rollerwhose width corresponds to the width of the material web and whose axisis arranged parallel with the guide support 28. The spray extending overthe width of the material web is created in that the liquid placed onthe surface of the roller is sprayed by the rapid rotation of theroller, and this sprayed liquid exits through a slit-shaped opening,whose slit width corresponds to the width of the material web.

A further possible spray device consists of individual spray nozzlesarranged next to each other, whose sprays together cover the width ofthe material web.

The method for monitoring the amount of liquid sprayed in the widthdirection operates as follows:

Initially, the counting device 18 is cleaned by means of the cleaningdevice 22, in that by means of the compressed air exiting the nozzle 62,dirt is directly blown off the counting device 18, in particular theoptical device of the counting device 18.

Thereafter the counting device 18 is brought into the test positionrepresented in FIG. 1, in which the laser beam 44 passes through theopened perforated screen 54 and illuminates the disk 64. The surface ofthe disk 64 has a reflecting coating. Then the laser beam 44 isinterrupted at a defined frequency by the rotating disk 64. When thelaser beam 44 is interrupted by the disk 64, a light reflection iscreated by the reflecting surface of the disk 64. The reflected light 46is bundled by the lenses 34 and 36 and imaged on the photodiode 40. Thephotodiode 40 generates a signal, which is supplied to the amplifier 48to be amplified and differentiated there and subsequently sent on to thecomparator 50. The comparator 50 then passes one pulse per signal on tothe evaluation unit. The pulses received by the evaluation unit 20 arecompared with the angular speed of the disk 64, so that it can bedetermined whether every reflex of the laser beam 44 had beenregistered.

A first measurement pass is started after the function test has beenperformed. To this end, the counting device 18 is brought into a firstmeasuring position along the guide support 28, so that the countingdevice 18 can cover the first measurement area 1. To this end, theperforated screen 55 is opened, so that the laser beam 44 illuminatesthe first measurement area 1. The light 46, reflected by the individualdroplets 16 flying through the first measurement area 1, is nowregistered by the counting device 18 and, as described above, providedto the evaluation unit 20 as an electrical pulse per passing droplet 16(see FIG. 3). The number of drops per unit of time, preferably 1.7 sec,is now counted in this way. An average value is determined from six suchmeasurements in the evaluation unit 20, which represents the localdroplet flow for the first measurement area 1. The droplet flow value isstored as a set value for the first measurement area 1 in the evaluationunit 20.

Only the droplets 16, which fly by the counting device 18 in a workingarea A, are optically detected in the course of registering the droplets16 by the counting device 18. The working area A is defined by theopening of the screen 38. Therefore the distances between the countingdevice 18 and the individual measurement areas are the same for allmeasurement areas and are matched to the opening of the screen 38, sothat the fan-like spray areas lie within the working area A.

The perforated screen 55 is now closed again and the counting device 18is moved to the second measurement area 2. A set value in relation tothe measurement area 2 is determined and stored in the same way. The setvalues for the further measurement areas, only a third one isrepresented in FIGS. 1 and 2, are also determined and stored.

If the material web 14 is intended to be moistened over its entire widthB, a check is now advantageously made to determine whether the setvalues of the individual measurement areas do not deviate too greatlyamong themselves. If the deviation is too great, it is a sign that thespraying device 12 is not operating correctly, for example because arotatable disk 102 is defective.

The counting device 18 is again moved into the first measurementposition after this, and a local droplet flow is again measured in thefirst measurement area 1 and stored in the evaluation unit 20.Afterwards the further measurement areas 2 and 3 are covered.

After this passage, the measured droplet flow values of the threemeasurement areas are compared with the corresponding set values in theevaluation unit 20. If, for example, the measured droplet flow of thesecond measurement area 2 deviates past a predetermined tolerancethreshold from the second set value, a signal, for example a warninglight, is preferably actuated. The operator of the device can thenimmediately determine that too little liquid has reached the materialweb in the measurement area 2, i.e. that the spraying device 12 operatesincorrectly in this area.

After this passage, the droplet flows of the individual measurementareas are measured during repeated passages and compared with the setvalues after each passage. A continuous check of the amount of liquidsprayed on the material web is provided in this way. Alternatively it isalso possible to compare the respectively measured droplet flow with theassociated set value immediately after it has been detected.

Correct positioning into the test and measuring positions of thecounting device 18 on the guide support 28 is respectively performed bymeans of an inductive switch, not represented.

It should be noted that it is not possible to draw conclusions regardingthe absolute amount of liquid sprayed in the associated fan-shapedsector by means of the number of droplets measured in respect to onemeasurement area. However, the method with accordance with the presentinvention is excellently suited to monitor the sprayed-on amount ofliquid, in that, starting from local set values once established, theinstantaneous local droplet flow values are measured and compared withthe set values, i.e. it is only possible to make relative statementsregarding the amount of liquid to be monitored.

For this reason, if the amount of liquid sprayed during one passage ischanged, it is no longer possible to make a comparison of the measureddroplet streams with the set values. A change in the amount of liquidsprayed is necessary, for example if, after a change of its conveyingspeed, the material web 14 is to be moistened with the same amount asbefore. However, reduced monitoring is nevertheless possible in thatonly the presence of local droplet flows in the individual measurementareas is registered. Then the rotatable plates 102 of the sprayingdevice 12 are only monitored for a total outage. It is recommended todetermine new set values at the termination of the monitoring passage.

The counting device 18 is cleaned and functionally checked at the end ofthe monitoring process, i.e. at the termination of all passages.

I claim:
 1. A method for monitoring the amount of moisture sprayed on amoving material web across its width, comprising the steps of:measuringa local droplet flow of the sprayed liquid for individual measurementareas over the width of the material web, respectively; storing themeasured values of the local droplet flow as set values; and againmeasuring the local droplet flow of the sprayed liquid in the individualmeasurement areas over the width of the material web and comparing thesemeasurements with said set values.
 2. The method as defined in claim 1,wherein the individual measurement areas are sequentially covered inorder to determine their local droplet flows.
 3. The method as definedin claim 1, further comprising the step of:comparing the stored setvalues with each other.
 4. The method as defined in claim 1, furthercomprising the step of:measuring and comparing the local droplet flowsin each measurement area with the initial set values repeatedly.
 5. Themethod as defined in claim 1, wherein each measured local droplet flowis compared with its associated set value immediately after it isdetermined.
 6. The method as defined in claim 1, further comprising thestep of:generating a signal if after any comparison a deviation isdetected between the measured value and the associated set value.
 7. Themethod as defined in claim 1, wherein the local droplet flows in therespective measurement areas only are measured after the amount ofliquid sprayed is changed.
 8. A device for monitoring the amount ofmoisture sprayed on a moving material web across its width, the widthbeing divided into individual measurement areas, comprising:a countingdevice; means for mounting said counting device and positioning itrelative to each individual mesurement area; and an evaluation unit,said counting device registering droplets of the liquid sprayed on themoving material web in a respective one of the individual measurementareas and generating a signal per registered droplet which is suppliedto said evaluation unit.
 9. The device as defined in claim 8, whereinsaid counting device includes optical means and wherein saidregistration is an optical registration.
 10. The device as defined inclaim 8, wherein said counting device includes a laser for illuminatingthe measurement areas, and a photodiode which detects the laser lightreflected by the droplets flying by.
 11. The device as defined in claim8, further comprising:perforated screens associated with eachmeasurement area situated between said counting device and the sprayedliquid.
 12. The device as defined in claim 11, further comprising:meansfor covering said perforated screens.
 13. The device as defined in claim8, further comprising:a cleaning device for cleaning said countingdevice.
 14. The device as defined in claim 13, wherein said cleaningdevice uses compressed air to clean said counting device.
 15. The deviceas defined in claim 8, further comprising:a testing device for testingthe function of said counting device.
 16. The device as defined in claim15, wherein said testing device includes a disk with concentricallyarranged openings, said disk being rotated at a defined angularvelocity, wherein said counting device includes a laser for illuminatingthe measurement areas, and wherein the rotation of said disk is suchthat it interrupts the light beam from said laser.
 17. The device asdefined in claim 8, further comprising:a guide support which extendsover at least the width of the material web, and wherein said countingdevice is mounted on said guide support to be longitudinallydisplaceable.
 18. The device as defined in claim 17, furthercomprising:a cleaning device for cleaning said counting device; and atesting device for testing the function of said counting device, whereinat least one of said cleaning device and said testing device are locatedat one end of said guide support.
 19. In an offset printing press havinga roller, a device for monitoring the amount of moisture sprayed on theroller across its width, the width being divided into individualmeasurement areas, comprising:a counting device; means for mounting saidcounting device and positioning it relative to each individualmeasurement area; and an evaluation unit, said counting deviceregistering droplets of the liquid sprayed on the moving material web ina respective one of the individual measurement areas and generating asignal per registered droplet which is supplied to said evaluation unit.20. In an offset printing press having a moving material web, device formonitoring the amount of moisture sprayed on the material web across itswidth, the width being divided into individual measurement areas,comprising:a counting device; means for mounting said counting deviceand positioning it relative to each individual measurement area; and anevaluation unit, said counting device registering droplets of the liquidsprayed on the moving material web in a respective one of the individualmeasurement areas and generating a signal per registered droplet whichis supplied to said evaluation unit.
 21. The device as defined in claim8, wherein the material web is one of a textile material web, a foilweb, a non-woven web, and a cellulose-containing material web.